Evacuated lightning arrester with series connected resistor



15, 1967 E. SARBACH ETAL 3,336,5QQ

EVACUATED LIGHTNlNG ARRESTER WITH SERIES CONNECTED RESISTOR Filed April 12, 1965 INVENTORS Ewql d urbach BY Em/L5 ucler United States Patent 3,336 500 EVACUATED LIGHTNING ARRESTER WITH SERIES (IONNETED RESISTOR Ewald Sarbach and Emil Studer, Baden, Switzerland, as-

signors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Filed Apr. 12, 1965, Ser. No. 447,185 Claims priority, application Switzerland, Apr. 16, 1964, 4,907/64 1 Claim. (Cl. 315-59) ABSTRACT OF THE DISCLOSURE A lightning arrester includes an electrically conductive metallic walled vessel in which are located a pair of spaced electrodes constituting a quench gap connected in series with a voltage-dependent resistor. An initially hollow, electrically conductive metallic stem extends into the vessel through its cover member and from which it is insulated, to enable the interior of the vessel to be evacuated. The lower end of the stem is electrically connected to one electrode, the other electrode is connected to one side of the resistor, and the other side of the resistor is electrically connected to the bottom wall of the vessel. After evacuation, the stem is closed oif and the terminal end of a connecting cable is fitted into and secured to the stem outwardly from its closed-01f point.

The present invention relates to lightning arresters and more particularly to an improvement in arresters of the type which have the quench gap located within an evacuated housing.

With arresters of the general type described, it is known to place the quench gap structure within a gas type housing and to lower the pressure thereinto an order I of from 10- to Torrs (Hg/cm?) in the space between the electrodes forming the quenching gap in order to increase the quenching capacity of the arrester. However, the production of such arresters requires an extremely careful, and therefore expensive, method of manufacture. Moreover, the voltage-dependent resistor units which are conventionally connected in series with the quench gap must be located within a separate housing, for example, an insulating cylinder, and vacuum-tight ducts are required in order to establish the necessary electrical connections between the resistor units and the electrode structure forming the quench gap.

The general object of the present invention is to provide a more simplified design and construction for a lightning arrester of the general type described and which is more economical to manufacture. In accordance with the invention, the quench gap and the series connected voltage-dependent resistor unit are located in a common, gas-tight vessel which is evacuated through a pumping stem, this-stem then serving as the means for electrically connecting the arrester unit to the circuit or apparatus to be protected by the arrester.

The invention will become better understood from the following detailed description of one suitable embodiment thereof and the accompanying drawing, the single figure of which shows the improved arrester in a central longitudinal section.

With reference now to the drawing, the arrester structure, which is a figure of revolution about the longitudinal axis, includes a quench gap established by and between spaced electrodes 1, 2 which are spaced apart by an annular disc 3 of insulating material, the two electrodes having confronting striking surfaces located in the central opening in disc 3. The lower electrode 2 rests upon a voltage-dependent resistor unit 4 which in turn rests upon the bottom of an essentially can-shaped metal vessel 5 which encloses the electrodes and resistor unit. Vessel 5 is closed in a gas-tight manner by means of an annular cover member 6. A glass-metal type of seal 7 located centrally within cover member 6 serves as a gas-tight lead-through and support for a hollow pumping stem 8 made of electrically conductive metal which extends downwardly through the cover and through a central opening in the upper electrode 1 into chamber 9 between the electrodes 1, 2. The lower end of stem 8 which is flared, is secured to and thereby also electrically connected with electrode 1.

The improved arrester structure according to the invention is assembled in the following manner. First, a sub-assembly consisting of the voltage-dependent resistor 4, lower electrode 2, centering disc 10 and insulating disc 3 is placed within the vessel 5 which at that time is fully open at the top. The diameter of centering disc 10 is preferably chosen as only slightly less than the internal diameter of the cylindrical vessel 5 so as to center this sub-assembly Within the vessel. A second sub-assembly consisting of the upper electrode 1, pumping stem 8, glass-metal seal structure 7 and cover plate 6, which latter also has a diameter only slightly less than the internal diameter of vessel 5, is then put in place, and the peripheral portion of the cover plate 6 is then soldered to the inside Wall of vessel 5 so as to establish a gas-tight seal. The upper end of pumping stem 8 is then connected to a suitable pump and the interior of vessel 5 is then pumped down to a suitable value corresponding to the desired response voltage of the arrester at which the gap between electrodes 1 and 2 will be bridged. For example, the interior of vessel 5 can be pumped down to a vacuum level between 100 and 400 mm. of mercury (Hg) after which pumping stem 8 is then pinched and sealed off 1 above cover plate 6, as shown in the drawing, by suitable pincer means.

Finally, after stem 8 has been pinched and sealed oif, a connecting cable such as cable terminal part 11 is then inserted into the upper end of hollow stem 8 above the sealed-off point and the stem pinched around the cable part 11 to establish a good mechanical and electrical connection therebetween.

In addition to the very simple and space-savings construction as well as the simplified mode of assembly, another advantage of the improved arrester structure lies in the fact that the previously encountered tolerance problem of the striking distance of the quench gap is eliminated to a great extent by virtue of being able to adjust the striking voltage, i.e. the voltage at which the gap between electrodes 1 and 2 breaks down, merely by an adjustment in the vacuum within the arrester vessel 5. This is particularly important when relatively low operating, or striking, voltages are involved, in which case the striking distance between the electrodes 1 and 2 must be very small, a condition which could only be achieved prior to this invention by a very accurate and therefore correspondingly expensive manufacturing method. However, with the improved arrester construction according to the invention, greater striking distances can be provided for low operating voltages, and minor differences in manufacture can be compensated out by adjustment of the degree of the vacuum produced within the vessel when pumping it down.

The improved lightning arrester is highly suitable for protection of regulating windings in transformers, induction coils and the like, since it can be readily installed in the tank of the apparatus to be protected. In this way, it becomes possible to replace lightning arresters which, up to now, have been arranged outside of the apparatus and which, in most cases, have required special ducting.

3 We claim:

In a lightning arrester, the combination comprising an evacuated gas-tight vessel, a voltage dependent resistor located Within said vessel and in contact with the bottom wall thereof, a pair of electrodes spaced apart by an insulating disc and located within said vessel With one of said electrodes in contact with said voltage-dependent resistor, a cover member secured to said vessel above said electrodes, an electrically conductive pumping stem extending through said cover member, one end of said pumping stem being connected to the other of said electrodes and the other end thereof being connectible to a vacuum pump for pumping down the interior of said vessel to the desired vacuum level, said pumping stem being thereafter closed oil at a point eXteriorly of said cover member to seal off the interior of said vessel, and a connecting cable including a terminal portion thereof fitted into and secured to said pumping stem outwardly from said closed off point.

References Cited UNITED STATES PATENTS 2,667,593 1/1954 Doolittle 313--7 X 2,703,852 3/1955 Meador 315-58 X 3,154,718 10/1964 Yonkers et al 3l558 DAVID J. GALVIN, Primary Examiner. 

